1. Studying emission mechanisms of AGN Dr. Karsten Berger Fermi School, June 2013 1 ©NASA

2. Motivation 2

3. 3 Cen A

4. What is an AGN made of? 4

5. Blandford-Znajek process Remember: black holes don‘t have hairs!!! 5

6. Which particles dominate in the jet? For simplicity: usually only leptons are considered in the models Should include protons, and thus also Muons, Pions… Synchrotron radio from e+/e-, µ+/µ- Inverse compton, external compton Pion decay… The exact jet composition is still under study 6

7. Two Blazar classes 7 BL Lac objectFlat spectrum radio quasar

8. Wehrle et al. 1998 x100 3C279 (z = 0.536) Flat spectrum radio quasar (FSRQ) Brightest AGN detected by EGRET (but see Fermi) Very strong flares in 1991 and 1996 low states in 1992 and 1997  Variable on a scale of ~ 100  Apparent luminosity ~ 10 48 erg/s  Fast time variation  T ~ 6hr in 1996 Strong absorption in very-high-energy (VHE): E  > 100 GeV: VHE discovery by MAGIC in 2006 Second flare in 2007 8

9. 9 Light curve 2007: Again no direct correlation, but delayed emission. Different emission regions?

10. Spectrum 2007 10 Very hard spectrum confirmed, photon index consistent with 2006 observations within errors (grey band corresponds to varying cut efficiencies)

11. SED 2007: two zone SSC model 11  Unfortunately no FERMI data yet  Blue line: emission inside the BLR  Red line: external compton emission outside the BLR  Pro: acceptable fit to the data, VHE emission region outside of dense photon fields: no problems with absorption  Con: twice the number of model parameters, more freedom

12. SED 2007: lepto-hadronic model 12  Considers not only leptons but also protons in the jet  Synchrotron emission from electrons/protons   -rays from pion decay (p- p-collisions)  Pro: can also reproduce the data  Con: again large number of free parameters, many emission components

13. Model results 13  Results are rather different depending on the model  A general trend: hadronic models have lower B and higher doppler factors  This leaves us the problem that we still cannot precisely determine the physical properties in the AGN, since several solutions are viable  More observations are needed, especially short term variability can help